The present invention relates in general to a system for magnetic tape head alignment. More particularly, the invention pertains to an improved magnetic tape alignment head and associated method of head alignment.
Digital magnetic tape recording and readout equipment is extensively used as a computer peripheral for information interchange with the computer. In order to render the recording medium compatible with different tape drives, the tape drive, such as one handling the standard half inch magnetic tape, must have the capability of recording data at the prevailing data packing density and track spacing with sufficient accuracy. In particular, the recorded data has to be capable of being reliably recorded when the recording medium is read out on equipment other than that on which it was recorded. As packing densities increase, greater performance demands are placed on the equipment used for data recording as well as data readout. Present day commercially available equipment is supposed to be capable of producing recording medium that is compatible throughout the industry. However, the degree of compatibility depends largely on the calibration procedures, the equipment that is used, such as calibration tapes, and the accuracy of measurements of the parameters that are involved.
Many tape-based storage devices and most disc-drive devices have only one signal path for data recovery. In these devices, reliable data recovery requires that the magnetic transducer gap be oriented normal to the path of media travel.
In connection with multi-track magnetic recording/reproducing devices, they typically used a skew tape which is used in the calibration and alignment of a magnetic recording/reproducing head. These heads are typically used on tape drives used in the computer industry for data storage, although they may also be used in connection with any other magnetic recording device. In these multi-channel magnetic storage applications, a high degree of head alignment accuracy is desired in order to maintain the data interchangeability. This is achieved by passing a skew tape under the read head to be aligned. The edge tracks are read as is illustrated hereinafter and the head is adjusted mechanically so that the analog signals of both tracks are superimposed, or in other words, so that the time difference between peaks is zero. The signals of all tracks are thus in phase with those of the edge tracks. This method is accurate and practical in achieving and maintaining data interchangeability in the industry using four, seven, and nine track read/write heads.
In connection with the known form of azimuth alignment, reference is made now to FIGS. 1A-1C. The azimuth alignment of a magnetic recording/reproducing head is a mechanical adjustment. FIG. 1A shows a prior art connection of read amplifiers along with an oscilloscope for displaying the waveforms of the outside tracks showing the skew or time difference between peaks which are being measured. FIG. 1B illustrates the proper position without skew in which all of the peaks align while FIG. 1C shows the signals from the outside tracks such as track 9 in comparison with the reference signal shown in solid as, for example, track 1. In the example that is given, the magnetic tape is considered as being a 9-track tape for use with a 9-track head. In FIG. 1C, the track is represented by dotted lines in different waveforms spread on both sides of the perpendicular X.sub.0. FIG. 1C illustrates the dynamic skew or jitter of the outside track about the reference which is to be measured with accuracy in order to align the head accurately. Visually, the extreme position of the positive peaks of the waveform are located at (+x) and (-x). These values can be added algebraically to obtain the average position of the head or average skew.
In addition to multi-channel, multi-head systems, single track or serial storage devices have now become more extensive in use and require a different procedure because no other channel exists with which to make a phase comparison. In this connection, in these single head systems, high track densities are achieved by stepping either a single or double read/write track head across the width of the tape. Whether a single or double track head is used, only one read and one write amplifier is available in such systems. Therefore, the method used with a standard 4, 7, or 9-track format for achieving azimuth alignment is not usable. However, the requirement for data interchangeability remains. Stated in another way, the convenience of reading two signals and adjusting for zero time difference between pulses or peaks of the two signals, is no longer available with the use of the single read/write amplifier arrangement.
The technique that is presently used to azimuth align a read head is to pass a tape under the single read track head and rotate the head clockwise and counter clockwise until the position is found where maximum output is obtained. The head is then secured. This method has drawbacks associated therewith. It requires that the skew tape be recorded with very high frequency signals in order to achieve acceptable tolerances. However, a skew tape recorded with these high frequencies is much more difficult to manufacture and test. Also, once the head position of maximum output is found, an error can be made quite easily when one attempts to secure the head with a screwdriver or other mechanical tool. This is apt to cause a change in the position, thus requiring recalibration.
Accordingly, it is an object of the present invention to provide an improved system for tape head alignment.
A further object of the present invention is to provide an improved system in accordance with the preceding object and which is particularly adapted for head alignment in a system employing a single movable tape head.